This invention relates to a roof support unit for use in a mineral mining working.
The roof of a mineral mining working, such as a longwall working, is usually supported by a roof support assembly constituted by a plurality of roof support units positioned side-by-side along the working. Typically each of the roof support units has a roof shield supported by means of hydraulic props on a floor sill. A goaf shield is provided between the floor sill and the roof shield at the goaf ends thereof.
When such a roof support unit is to be used to support the roof of a mine working of varying seam height, it is necessary for the props of the unit to be able to support the roof over a relatively wide range of seam heights. One way of accomplishing this, without having very large props, is to incline one or more of the props towards the face being won, and one or more of the props towards the goaf side of the working. In known arrangements of this kind, the prop(s) inclined towards the face engage the roof shield, whereas the prop(s) inclined towards the goaf side of the working engage the goaf shield. Although such an arrangement results in sufficient roof supporting force to be achieved over the desired range of seam heights, it suffers from the disadvantage that the forces acting on the goaf shield impose an extremely heavy load on the link between the goaf shield and the roof shield. Moreover, use must be made of props of different lengths which is detrimental from the point of standardisation of equipment. Furthermore, the goaf shield is used to support part of the force exerted by the roof of the working which is not desirable as the goaf shield is designed only to support the loads imposed by falling rubble. (A typical roof support unit of this kind is described in DT-Gbm No. 7602845).
The aim of the invention is to provide a roof support unit for use with seams of varying height and which does not suffer from these disadvantages.